Yang Yuanyuan, Zhang Jinchuan, Xu Longfei, Li Pei, Liu Yang, Dang Wei
School of Energy and Resources, China University of Geosciences (Beijing), Beijing 100083, China.
Key Laboratory of Strategy Evaluation for Shale Gas, Ministry of Natural Resources, Beijing 100083, China.
ACS Omega. 2022 Mar 14;7(11):9229-9243. doi: 10.1021/acsomega.1c05779. eCollection 2022 Mar 22.
Pore structure has certain significance for the preservation and enrichment of shale gas. However, less attention is paid to deep shale (>3000 m) which has unique pore characteristics that distinguish it from the shallow and medium layers. In order to study the pore structure characteristics of deep shale, 10 samples of the Shanxi Formation are collected from well YP-1 within the depth of 3550-3610 m in the Fuxian block of the Ordos Basin. The pore structure characteristics of shale samples are quantitatively studied by scanning electron microscopy (SEM), low-temperature nitrogen adsorption-desorption, and high-pressure mercury injection experiments. The pore surface area (SA) and pore volume (PV) of the deep shale of Shanxi formation are low, with average values of 4.282 m/g and 0.0126 mL/g, respectively. The content of total organic carbon (TOC) is high, which is in the high over mature stage, with undeveloped organic pores and developed microfractures. The main mineral components are clay (51.6%∼89.1%) and quartz (8%∼41.7%). By establishing the relationship between SA, PV, and TOC for quartz and clay minerals, it is found that these three parameters have little contribution to SA and PV. The pore diameter is mainly mesoporous, 2.5-4 nm and 8-11 nm. The complexity of pore structure is discussed through the fractal dimension calculated by the fractal Frenkel-Halsey-Hill (FHH) model. The pore fractal dimension (2.6240) is greater than (2.5608), and the complexity of the pore structure is greater than that of the pore surface. The fractal dimension of deep shale in Shanxi is negatively correlated with TOC content and weakly correlated with quartz and clay minerals. It shows that the mineral composition of deep shale in Shanxi Formation in the study area has little effect on pore development, and the development of microfractures is the main contribution of SA and PV.
孔隙结构对页岩气的保存和富集具有一定意义。然而，人们对深部页岩（>3000米）关注较少，深部页岩具有独特的孔隙特征，使其有别于浅部和中部地层。为研究深部页岩的孔隙结构特征，从鄂尔多斯盆地富县区块YP-1井3550-3610米深度范围内采集了10块山西组样品。通过扫描电子显微镜（SEM）、低温氮吸附-脱附以及高压汞注入实验对页岩样品的孔隙结构特征进行了定量研究。山西组深部页岩的孔隙表面积（SA）和孔隙体积（PV）较低，平均值分别为4.282平方米/克和0.0126毫升/克。总有机碳（TOC）含量较高，处于高过成熟阶段，有机孔隙不发育，微裂缝发育。主要矿物成分为黏土（51.6%∼89.1%）和石英（8%∼41.7%）。通过建立石英和黏土矿物的SA、PV与TOC之间的关系，发现这三个参数对SA和PV的贡献较小。孔径主要为中孔，2.5-4纳米和8-11纳米。通过分形Frenkel-Halsey-Hill（FHH）模型计算的分形维数来探讨孔隙结构的复杂性。孔隙分形维数（2.6240）大于孔隙表面分形维数（2.5608），孔隙结构的复杂性大于孔隙表面。山西组深部页岩的分形维数与TOC含量呈负相关，与石英和黏土矿物呈弱相关。这表明研究区山西组深部页岩的矿物组成对孔隙发育影响较小，微裂缝的发育是SA和PV的主要贡献因素。
